Importance of physical fitness on predictive effect of body mass index and weight gain on incident atrial fibrillation in healthy middle-age men.

The incidence of both atrial fibrillation (AF) and obesity is increasing in the community, and lifestyle intervention is recommended. We aimed to test whether the predictive effect of body mass index (BMI) and weight change from age 25 years to midlife on incident AF were influenced by physical fitness. In 1972 to 1975, 2,014 healthy middle-age men conducted a bicycle exercise electrocardiographic test as a part of a cardiovascular survey program, defining physical fitness as work performed divided by body weight. During 35 years of follow-up, 270 men developed AF, documented by scrutiny of the health files in all Norwegian hospitals. Risk estimation was analyzed using Cox proportional hazard models and tested for age-adjusted physical fitness above and below the median. The mean BMI of 24.6 kg/m(2) defined a lean baseline cohort. The men with a baseline BMI of ≥28 kg/m(2) (11%) compared to a BMI <28 kg/m(2) had a 1.68-fold risk of AF (95% confidence interval 1.14 to 2.40) and men reporting weight gain of ≥10 kg (24%) compared to weight loss (11%) of 1.66-fold (95% confidence interval 1.00 to 2.89), respectively. The dichotomy into men with age-adjusted physical fitness above and below the median, demonstrated statistically significant risk associations only for men with low fitness. The overall risk of AF was reduced by 23% in the fit men. In conclusion, within our lean baseline cohort of healthy middle-age men, a BMI of ≥28 kg/m(2) and weight gain of ≥10 kg from age 25 to midlife were long-term predictors of incident AF in men with physical fitness below the population median. The fit men had an overall slightly reduced risk of AF.